a(n) is the closest number to 2^n which is divisible by n.

Terms

a(0) =2a(1) =4a(2) =9a(3) =16a(4) =30a(5) =66a(6) =126a(7) =256a(8) =513a(9) =1020a(10) =2046a(11) =4092a(12) =8190a(13) =16380a(14) =32775a(15) =65536a(16) =131070a(17) =262152a(18) =524286a(19) =1048580a(20) =2097144a(21) =4194300a(22) =8388606a(23) =16777224a(24) =33554425a(25) =67108860a(26) =134217729a(27) =268435468a(28) =536870910a(29) =1073741820